Implantable or subcutaneous delivery devices have been known for the delivery of contraceptives in women for some time. Indeed, a number of devices have been used in subcutaneous contraception systems for women, including the much publicized NORPLANT.RTM. and NORPLANT II.RTM. systems. These systems involve implants composed of a silicone elastomer, such as, for example, SILASTIC.RTM., siloxane-containing material available from Dow Corning. See U.S. Pat. Nos. 4,957,119 and 5,088,505. The convenience and reliability of these systems render them desirable substitutes for other forms of chemical and mechanical contraception.
Of course, if similar systems could be provided for men, their convenience might encourage a greater portion of the already sexually active population to engage in contraception. However, the production of a subcutaneous male contraceptive is not without difficulty. One cannot merely administer compounds which block gonadotrophin secretion and sperm production, such as LHRH and its analogues, without also decreasing testosterone production. This can depress male sexual function which would undermine the advantages of using this type of system. Therefore, androgens must be an essential part of an overall male subcutaneous contraceptive strategy.
One possible answer involves the production of an implant system for administering both an androgen and a sterilant. One implant would be administered to a patient and would deliver an androgen such as testosterone or 7.alpha.-methyl-19-nortestosterone ("MENT") or its acetate derivative ("MENT Ac") to provide for normal male function. The same implant or another implant would administer a sterilant. The NORPLANT.RTM. system would seem a likely model for such implants. Unfortunately, when these silicone-based implants were investigated, considerable complications arose. In fact, a system using a silicone elastomer-based implant was found to be unsatisfactory. As noted in Sundaram et al., "7 Alpha-Methyl-Nortestoster-one(MENT): The Optimal Androgen For Male Contraception," Annals of Medicine, (1993), 25, 199-205, SILASTIC.RTM. based implants containing MENT had to be replaced at intervals of three weeks because of the rapid loss of androgen. Based on this discovery, it was concluded that androgen could not be administered from silicone elastomer containing implants in a long-term, practical, highly repeatable fashion.
It was subsequently discovered that androgen could be delivered alone for androgen therapy when done as part of an implant system using an ethyl vinyl acetate ("EVA") core and an EVA containing rate limiting coating. See U.S. Pat. No. 5,733,565. Of course, while this discovery was a significant breakthrough in male contraception, it is still desirable to identify other implant systems which could be useful for the delivery of androgen, either alone as part of androgen replacement therapy or in combination with a sterilant to maintain male cell sex function while providing contraceptive efficacy.